<PAGE>
 
                                                                EXHIBIT 10(a)(5)

                                FIFTH AMENDMENT

     FIFTH AMENDMENT, dated as of November 30, 1995 (this "Amendment"), to the
Credit Agreement, dated as of December 8, 1993 (as amended prior to the date
hereof and as further amended, supplemented or otherwise modified from time to
time, the "Credit Agreement"), among ICF KAISER INTERNATIONAL, INC. a Delaware
corporation (the "Borrower"), the lenders parties thereto (the "Lenders") and
CHEMICAL BANK, a New York banking corporation, as agent (in such capacity, the
"Agent").

                                  WITNESSETH:

     WHEREAS, the Company, the Lenders and the Agent are parties to the Credit
Agreement; and

     WHEREAS, the Company has requested that the Lenders and the Agent agree to
amend certain provisions of the Credit Agreement, and the Lenders and the Agent
are agreeable to such request upon the terms and subject to the conditions set
forth herein;

     NOW, THEREFORE, in consideration of the premises and mutual agreements
contained herein, and for other valuable consideration the receipt of which is
hereby acknowledged, the Company, the Lenders and the Agent hereby agree as
follows:

          1.   Definitions.   All terms defined in the Credit Agreement shall
have such defined meanings when used herein unless otherwise defined herein.

          2.   Amendment of Subsection 7.1.  (a) Subsection 7.1 of the Credit
Agreement is hereby amended by deleting such subsection 7.1 in its entirety and
inserting in lieu thereof the following new subsection 7.1:

     "7.1 Financial Condition Covenants.

     (a) Fixed Charge Coverage.  Permit, for each of (i) the fiscal quarters
ending on each of February 28, 1995 and May 31, 1995, (ii) the period of two
consecutive fiscal quarters ending on August 31, 1995, (iii) the period of three
consecutive fiscal quarters ending on November 30, 1995, (iv) the period, ending
on the Company's new fiscal year-end of December 31, 1995, comprised of the
three consecutive fiscal periods ending on November 30, 1995 and the calendar
month of December, 1995, (v) the fiscal period commencing on March 1, 1995 and
ending on March 31, 1996, (vi) the fiscal period commencing on June 1, 1995 and
ending on June 30, 1996, (vii) the fiscal period commencing on September 1, 1995
and ending on September 30, 1996, (viii) the fiscal period commencing on
December 1, 1995 and ending on December 31, 1996, and (xi) each period of four
consecutive fiscal quarters ending thereafter, the ratio of (i) sum of (A)
Adjusted Consolidated Net Income for such period plus (B) Consolidated Lease
Expense for such period minus (C) Capital Expenditures for such period to (ii)
the sum of (A) Consolidated Fixed Charges for such period plus (B) the aggregate
amount of dividends paid in cash on shares of each class of preferred Capital
Stock of the Borrower during such period, to be less than the ration set forth
opposite such Test Period below:
<TABLE>
<CAPTION>
                                                   Fixed Charge
                        Period Ending             Coverage Ratio
                        <S>                       <C>
                        February 28, 1995            1.00:1.00
                        May 31, 1995                 1.00:1.00
                        August 31, 1995              1.05:1.00
                        December 31, 1995            1.10:1.00
                        March 31, 1996               1.15:1.00
                        Thereafter                   1.20:1.00

</TABLE>
<PAGE>
 
     (b) Interest Coverage. Permit, for each of (i) the fiscal quarters ending
on each of February 28, 1995 and May 31, 1995, (ii) the period of two
consecutive fiscal quarters ending on August 31, 1995, (iii) the period of three
consecutive fiscal quarters ending on November 30, 1995, (iv) the period, ending
on the Company's new fiscal year-end of December 31, 1995, comprised of the
three consecutive fiscal periods ending on November 30, 1995 and the calendar
month of December, 1995, (v) the fiscal period commencing on March 1, 1995 and
ending on March 31, 1996, (vi) the fiscal period commencing on September 1, 1995
and ending on December 31, 1996, and (xi) each period of four consecutive fiscal
quarters ending thereafter, the ratio (the "Interest Coverage Ratio") of (A)
Adjusted Consolidated Net Income for such period to (B) Consolidated Interest
Expense for such period, to be less than the ratio set forth opposite the last
day of such period below:
<TABLE>
<CAPTION>
                         
                                             Interest
                Period Ending             Coverage Ratio
                <S>                       <C>
                February 28, 1995            1.40:1.00
                May 31, 1995                 1.45:1.00
                August 31, 1995              1.50:1.00
                December 31, 1995            1.60:1.00
                March 31, 1996               1.80:1.00
                Thereafter                   2.00:1.00

</TABLE>
     (c) Consolidated Funded Indebtedness to Consolidated Capital Funds.  Permit
the ratio of Consolidated Funded Indebtedness to Consolidated Capital Funds on
the last day of any fiscal quarter ending during any "Test Period" set forth
below to be greater than the ratio set forth opposite such period below:
<TABLE>
<CAPTION>
 
                Test Period                          Ratio
     <S>                                             <C>
 
     Closing Date through May 31, 1994               .76:1.0
     June 1, 1994 through November 30, 1994          .75:1.0
     December 1, 1994 through August 31, 1995        .78:1.0
     September 1, 1995 through December 31, 1995     .77:1.0
     January 1, 1996 through March 31, 1996          .76:1.0
     Thereafter                                      .75:1.0"
</TABLE>

          3.   Interpretation.  For avoidance of doubt in connection with
delivery of Applicable Margin Certificates, quarterly financial reports, and
certain representations and warranties, references in the Credit Agreement to
the "most recently ended" fiscal quarter or period (or similar formulation)
shall, after November 30, 1995 and before December 31, 1995, refer to the fiscal
year period ended on such date.  Financial statements will be delivered both for
the fiscal quarter ended November 30, 1995, and for the fiscal year period
ending December 31, 1995.

          4.   Representations; No Default.   On and as of the date hereof, and
after giving effect to this Amendment, the Company confirms, reaffirms and
restates that the representations and warranties set forth in Section 4 of the
Credit Agreement and in the other Loan Documents are true and correct in all
material respects, provided that the references to the Credit Agreement therein
shall be deemed to be references to this Amendment and to the Credit Agreement
as amended by this Amendment.

          5.   Conditions to Effectiveness.   This Amendment shall become
effective on and as of the date (the "Amendment Effective Date") that the Agent
shall have received counterparts of this Amendment, duly executed and delivered
by a duly authorized officer of each of the Company, the Agent, and the Required
Lenders, along with the written consent of each Subsidiary Guarantor in the form
attached hereto.
<PAGE>
 
          6.   Limited Amendment.   Except as expressly waived and amended
herein, the Credit Agreement shall continue to be, and shall remain, in full
force and effect.  This Amendment shall not be deemed to be a waiver of, or
consent to, or a modification or amendment of, any other term or condition of
the Credit Agreement or any other Loan Document or to prejudice any other right
or rights which the Lenders may now have or may have in the future under or in
connection with the Credit Agreement or any of the instruments or agreements
referred to therein, as the same may be amended from time to time.

          7.   Costs and Expenses.   The Company agrees to pay or reimburse the
Agent for all its reasonable and customary out-of-pocket costs and expenses
incurred in connection with the preparation, negotiation and execution of this
Amendment, and the consummation of the transactions contemplated hereby,
including, without limitation, the reasonable fees and disbursements of its
counsel.

          8.   Counterparts.   This Amendment may be executed by one or more of
the parties hereto in any number of separate counterparts and all of said
counterparts taken together shall be deemed to constitute one and the same
instrument.

          9.   GOVERNING LAW.   THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

          IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be executed and delivered by their respective duly authorized officers as of the
date first above written.